Purified and intact mitochondria isolated from potato tuber show a specific concanavalin A (Con A) binding as deduced from fluorescence labelling studies in the presence of the specific sugar α-D-methylmannose. This specific binding also occurs in mitoplasts, indicating the presence of Con A-binding sites on the inner mitochondrial membrane. In contrast, the binding of wheat germ agglutinin appears non-specific. Flow cytometry with purified mitochondria enables assessment of the binding by individual mitochondria. Thus, three mitochondrial subpopulations were identified by their reactivity towards fluorescent Con A.